Yup, and when it comes to the effects of moisture/humidity on contacts, it's not just coin cell holders either. Tabbed batteries soldered to the board would be great, but short of that, sealing the contacts with impermeable waterproof epoxy should--I'm hoping--also work (cf
https://lowpowerlab.com/forum/index.php/topic,243.msg11809.html#msg11809 ) In the end, though, I'm discovering that the epoxy cost may actually be more expensive than, or at least comparable to, buying new tabbed batteries.
Hence, I'm searching for a less costly way to weatherproof.